Fateman's work was a *Mathematica-to-Lisp* translator: quoting from that paper,
he wrote
"a Common Lisp program that can read (from a file or a keyboard) virtually
any Mathematica program or command, and will produce a Lisp data structure
closely resembling the FullForm printout of Mathematica."

It's also worth noting that Wolfram Research claims copyright over the
Mathematica language, and asserts that Fateman's translator infringed
that copyright. (Google 'Fateman Mathematica "Brown & Bain"' for a
letter from WRI's lawyers to Fateman claiming this.) I don't know the
exact boundary of how much of and/or how closely you can clone Mathematica
without getting into legal trouble.